Featured Article (August 2005)

Feed Supplements, Yours or Mine?

When conversation turns to feed supplements, what comes to your mind?

Heavenly herbs?

For horses we want leafy herbs, such as scull cap, red clover, Gotu Kola, Echinacea and gingko, preferably blessed by Chinese gods—Buddha, Kangzi and Cahng-fei. Europeans, especially Germans, take herbs for horses seriously and entreprenurally. Herb salespersons are abundant and aggressive at European equine expositions. Americans are no less gullible than Germans, so there must be a golden marketing opportunity for herbs here in the USA.

Nutraceuticals?

Nutrient products that play lightly around disease claims and escape Federal drug regulations are like SUVs. Sport utility vehicles are classified as light trucks hence escape the costly Federal car safety regulations, so can be made more cheaply hence more profitably. For the good of their share-holders, companies convince gullible people to buy huge SUVs to do the work of smaller cars. Similarly, companies manufacturing nutraceuticals avoid the huge regulatory expenses incurred by drugs, so can afford the costs of persuading nice people to use nutraceuticals instead of drugs.

The wide acceptance of certain nutraceuticals, notably glucosamine and chondroitin sulfate for pain and inflammation in joints, poses a conundrum. We all know highly competent horsemen (and dog handlers) who swear by the effectiveness of glucosamine and chondroitin sulfate. These positive testimonials should be weighed against the skepticism in recent systematic reviews (meta-analyses) in the human medical literature.

Then there’s the question of safety. Drugs must pass two tests, acute and chronic. And drugs must be made and packaged under stringent specified conditions. All of that safety cushion rolls into the price you pay for a drug. It’s clever price-wise to avoid those regulatory costs and qualify a drug-like product as a nutraceutical.

Dietary supplements?

In 1994, Senator Orrin Hatch (Rep., Utah) added to his many good works the Dietary Supplement Health and Education Act (DSHEA). The ostensible intention was to improve public health by relaxing the already loose regulations concerning vitamin and mineral supplements. The apparently unintended consequence was to let a burgeoning dietary supplement industry run wild. Walk along the aisle in your favorite feed store and see the impact of DSHEA on the horse scene—dozens of dietary supplements embroidered with extravagant health claims.

The FDA took the position that the laissez faire regulations in DSHEA would not apply to animals, reversing the traditional custom of consistency between food and drug regulations for animals and for humans. The FDA aspired to keeping the lid on the traditional categories of feed ingredients and feed additives, both distinct from drugs, that is, disease claims, but simply has not had the funds and manpower to pursue this worthy objective. Meanwhile, Senator Hatch turns all criticism of DSHEA pertaining to animals and people back on the FDA.

How does all of this political-industrial chicanery affect you and your horses? You have become victims. You would need a PhD with a major in nutrition and a minor in pharmacology to evaluate the vainglorious health claims on the labels of most dietary supplements. I could help with a few, like plain white salt.

Then it gets tough. For example, omega-3 fatty acids are being promoted for horses without mention of adverse effects on bleeding and wound healing, which have been demonstrated in several other species so are likely to occur also in the horse. Increasing doses of antioxidants in general improve then impair immunity, but there’s no dose-response curve determined yet for the horse.

Feed supplements?

A product you probably call a feed, such as Omolene-200™ (Purina Mills, St Louis, MO), in my mind is a supplement. It makes up the nutrients provided inadequately by the pasture or hay in the horse’s diet. If this feed is designed correctly as a supplement, then there is no need for further dietary supplements.

I mention the Purina product not to endorse it commercially but to remind us that it was a John Danforth, a forebear of today’s John Danforth (Missouri), who made a horse feed in the 1890s that was the first complete and balanced feed (or food) for any species. This horse feed was for the use of his friends "to take the worry out." That is exactly what a feed supplement should do also—take the worry out of feeding your horse. It is harder, however, to design a feed supplement than a complete and balanced feed, because the supplement must have flexibility built in to be mixed in various proportions with the staple, the pasture or hay.

Fortunately for horses and their care-givers, there are now many horse feed manufacturing companies that have competent equine nutritionists. These equine nutritionists formulate feeds as true supplements using their own target zones for nutrients, which are usually in the range of one-and-a-half to 3-times the average minimum nutrient requirements recommended by the National Research Council (NRC). Twenty and more years ago, there were few genuine equine nutritionists, and the market hardly warranted their employment, so most companies used a poultry, pig or ruminant nutritionist to formulate horse feeds based on NRC nutrient requirements instead of higher allowances or target zones. Thus horse feeds back then needed dietary supplements of minerals, vitamins and perhaps other nutrients, especially to sustain higher performance. For products from the better companies, this is no longer the case.

Minerals

My first research project at Virginia Tech and the Middleburg Agricultural Research and Extension Center (MAREC) was a survey of pasture composition and feeding practices on Thoroughbred farms in central and north-central Virginia. Clearly there was marginal phosphorus and deficiencies of sodium, copper, zinc and selenium.

To formulate minerals in MAREC feeds, we borrow a statistical method from economics, sensitivity analysis, which evaluates reasonable upper and lower limits as well as the middle value. We balance ranges of mineral concentrations and pasture intakes against target ranges for horses. These target ranges taken into account ranges of horse sizes and activities and digestive/metabolic efficiencies.

Too much arithmetic? We don’t know anybody else who takes this much trouble, but sensitivity analysis should be applied in every region that has its own coherent set of mineral analyses. Selenium distribution is patchy, with toxicity the problem in Utah in contrast to deficiency in Virginia. Much of western Europe has too much phosphorus, so the MAREC mineral mixture would be inappropriate. The Russians claim that their regional dispensatoriums of minerals for horses won World War II. The Soviet horses remained strong and kept on pulling the supply wagons carrying food and ordnance through the soggy lands of the Ukraine, while the German horses grew weak and bogged down on the way to Kiev and Moscow.

Our students found that intakes of minerals were reflected in concentrations in blood plasma, with one exception. Plasma phosphorus is high in phosphorus deficient pregnant mares. Their urine also contains much phosphorus and calcium. The most likely explanation is that the pregnant mare with a low phosphorus intake mobilizes phosphorus and calcium from her bones to ensue an abundant supply for her fetus.

On hearing about our mineral results 15 years ago, the manager of a large farm asked me to formulate a mineral supplement to be used with his pasture and grain-based feed. I complied and included a little blue plastic scoop in each bucket. The farm had six large barns with 20 or more horses per barn. I lectured the staff on the need to use the scoops to keep the minerals in optimal ranges—both too little and too much were equally bad. A month later I visited the farm and found one dusty blue scoop on a nail in one barn, that’s all.

About 12 years ago I was invited to consult on a nutritional problem in about 20 yearlings. They were fed a dietary supplement in the form of potent pellets placed in buckets hung along a fence 8 feet apart. After a thorough mathematical analysis, I told the manager that affected yearlings must be consuming twice the intended dose. He was offended and swore that each yearling consumed pellets only from its own bucket, according to his assistants. I said that the mathematic analysis was incontrovertible and recommended a feed supplement that would provide the same doses or minerals at lower concentrations.

While he was temporarily stunned by that "incontrovertible" I reminded him that the two most dangerous items on his kitchen table were salt and sugar, both over 99% pure chemicals. One must be more careful with butter and whisky than with milk and beer, I continued. The same principal applies to concentrated dietary supplements and potent pellets versus dilution of potentially toxic nutrients in a specifically formulated feed. "I’d like to offer your yearlings all of their essential nutrients in 4 pounds of feed than in 4 ounces of potent pellets," I said.

Vitamins

Vitamins are hard to measure, so hard to study, and if you must know the truth equine science is rather thin on vitamins. Our graduate students conducted experimental studies on vitamins. They found that intakes of vitamins, unlike minerals, were not reflected in concentrations in blood plasma. Deficiencies were revealed, however, by function tests—vitamin A by the dose-response test, folacin in plasma homocysteine, and vitamin E by antioxidant status. They found that supplementation with vitamin A itself would reverse the adverse effects of vitamin A depletion on reproductive efficiency and the body weight of foals. Also vitamin E supplementation for 3 weeks before an endurance race decreased oxidative stress. We’ve also assayed vitamins A and E in the blood of mares and newborn foals, and in colostrum and milk. On the basis of all of these studies, we have raised the lower limit of our target zones for these vitamins to twice the NRC minimum nutrient requirements.

Protein

The prices of horse feeds are tied to protein contents, tradition prevailing over nutritional science. The MAREC targets for protein are around 16% of dry matter for tissue build-up (predominantly anabolic) conditions, such as growth, pregnancy and lactation, and around 10% for tissue breakdown (mainly catabolic) conditions. The protein content of pasture "typically" ranges from about 25% of dry matter in the spring and early summer to about 10% in the fall and winter. By "typically" I mean according to most books. At MAREC we have these "typical" seasons about once every five years. More often we enjoy intermittent warm rains that stimulate growth and keep pasture protein bouncing between 20 and 25%. So how much protein do we need in the MAREC feed supplements? You’re right, it’s easy, the answer is not much.

There are two special situations requiring extremely high quality protein—the top performance athlete and the emaciated, decrepit old horse. We have persuasive data showing that metabolic efficiency is enhanced by adapting horses performing repeated sprints to a 9% extremely high quality protein complete feed. The high quality was achieved by fortification with limiting amino acids—lysine and threonine.

We have no statistically useful data on old horses but much experience. When we started at MAREC, many donated mares were old and infertile. A group of a dozen or so barren mares would be kept on winter pasture with a round bale of hay. Most would be plump, a body condition score of 6 or 7, but one or two or three would become thin, body condition score of 2 or 3, despite the abundance of food.

We suspected by analogy with other species that these thin old mares might have lost their appetite due to protein deficiency, so they might respond to protein supplementation. From my experience with the nutritional support of hypermetabolic sick horses, we tried Calf Manna™ (Manna-Pro Coop., Chesterfield, MO) mixed half-and-half with our usual non-experimental feed. Calf-Manna has about 25% high-quality protein and a harmonious blend of ingredients that suits horses. A graduate student would hand-feed 3 pounds of this mixture twice a day. The response is highly repeatable. After a few days, the mare’s appetite improves, and she starts to nibble pasture and hay. She takes 3 or 4 months to build back to a body condition score of 4 or 5.

We repeated this experience with much larger numbers on a nearby retirement farm. We failed, however, to perform a controlled comparative trial of, say, 20% versus 10% protein supplement for the usual reason—a tender heart.

Energy sources

Energy is the capacity to do work, indeed its unit, the erg, means work. Material sources of potential chemical energy in foods, feeds and forages are proteins, fats and oils, and carbohydrates—such as starches, sugars and fibers. We usually neglect proteins, however, when speaking of feed energy sources, because proteins are utilized inefficiently and create extra work for the liver and kidneys.

The main energy sources for horses during their evolution were forages rich in fibers—notably, cellulose and hemicellulose, which are insoluble, and fructan, which is soluble in water. These fibers are not digested by mammalian enzymes. Instead, they are fermented by microbial enzymes, mainly in the large bowel. This process is inefficient, so that about 50% of the gross intake energy is lost as feces, gas and heat. This heat is useful in winter but not summer.

Three centuries ago, the practice of feeding grain to horses greatly increased, and during the 20th century molasses was added to grain mixes to make "sweet feed." Starch in grain and sugar in molasses are digested by mammalian enzymes in the small intestine to yield glucose—up to a poorly defined limit, usually between 50 and 75% of the dietary dry matter. Above this limit, the overload proceeds to the cecum, where it is welcomed by the microbes, who run riot. Rapid fermentation produces excessive amounts of acid and gas, which may lead to some forms of diarrhea, colic, colitis and laminitis.

Sweet feed is utilized much more efficiently than fibrous forages, with an energy loss of only 15 to 25%. Thus the use of sweet feeds can enable a much higher energy output than is possible with forages only. The more sweet feed, the higher performance, up to that poorly defined upper limit. Do you wait until you see colic or diarrhea? Or do you back off before that?

Back off until sweet feed provides only about one-third of the ration, and the horse is still in trouble, albeit not obviously. Each meal of 4 pounds or more releases so much glucose that it causes a huge bump in blood concentrations of glucose and insulin. The cumulative effect is the development of chronic insulin resistance, which is a risk factor for many diseases. The most frequent in humans are diabetes mellitus-2, coronary disease, stroke and certain kinds of cancer. The most frequent in horses are some forms of exertional rhabdomyolysis, developmental orthopedic disease, hyperlipidemia and laminitis.

These equine grain-associated disorders were suspected by yours truly when he was Chief of Medicine at New Bolton Center. The opportunity to test these ideas was one of the main attractions of the job of Research Director, MAREC. After 17 years and on the verge of retirement, I am satisfied that the major achievement of my tenure at MAREC has been the development of feed supplements based on fat (actually vegetable oils) and fiber (actually sophisticated carbohydrate profiles) instead of starch and sugar. These fat-and-fiber feeds all contain about 12% of vegetable oil, because that results in maximal muscle glycogen content and improved energetic efficiency. They vary in their carbohydrate profiles, however, with different designs for specific purposes, for example, growth or repeated sprints. These carbohydrate profiles have some proprietary value that Virginia Tech shares with the sponsors of our graduate student training program, the WALTHAM Centre for Pet Nutrition, Melton Mowbray, UK (a division of Mars, Inc., McLean VA).

Acknowledgements

Our thanks are due to MAREC’s singular benefactor, the late Paul Mellon. Upperville, VA, a second major Anonymous Benefactor, the John Lee Pratt Program in Nutrition, the Virginia Thoroughbred Association, the Virginia Horse Industry Board, the Bernice Barbour Foundation, and the WALTHAM Centre for Pet Nutrition. My thanks are also offered to 24 graduate students, the main energy source of MAREC, and to administrators, faculty and staff who have acted as supplements.

David S. Kronfeld, (MA(hc), PhD, DSc, MVSc, DipACVIM, DipACVN, is the retiring Paul Mellon Distinguished Professor of Agriculture, and Professor of Veterinary Medicine, and the Research Director of the Middleburg Agricultural Research and Extension Center,Virginia Polytechnic Institute and State University, Allover, VA.